Transformer with magnetic shields



Oct. 13, 1970 c, J, BELL 3,534,311

TRANSFORMER WITH MAGNETIC SHIELDS Filed April 9, 1969 4 Sheets-Sheet lFIG. I.

FIG. IA.

WITNESSES INVENTOR jz zna g m Clifford J. Bell ATTORNEY Oct. 13, 1970 c.J. BELL 3,534,311

TRANSFORMER WITH MAGNETIC SHIELDS Filed April 9, 1969 4 Sheets-Sheet 2Oct. 13, 1970 1 E L 3,534,311

TRANSFORMER WITH MAGNETIC SHIELDS Filed April 9, 1969 4 Sheets-Sheet sOct. 13, 1970 c. J. BELL 3,534,311

TRANSFORMER WITH MAGNETIC SHIELDS Filed April 9, 1969 v 4 Sheets-Sheet 4/lll United States Patent O 3,534,311 TRANSFORMER WITH MAGNETIC SHIELDSClifford J. Bell, Muncie, Ind., assignor to Westinghouse ElectricCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr.9, 1969, Ser. No. 814,637 Int. Cl. H01f 15/04 U.S. Cl. 33684 8 ClaimsABSTRACT OF THE DISCLOSURE An electrical transformer of the shell-formtype having a plurality of coils disposed in inductive relation with amagnetic core structure. The electrical transformer includes magneticshielding members disposed to provide low reluctance magnetic circuitsfor the leakage flux of the coils. Certain of the magnetic shieldingmembers are formed of a cast insulating resin filled with magneticmaterial. These cast magnetic shielding members are utilized adjacentthe curved portions of the coil openings, and are cast to substantiallythe configuration of the opening it is to fill, to increase the volumebetween the coils and the magnetic core which is filled with magneticmaterial.

CROSS-REFERENCE TO RELATED APPLICATION Certain of the apparatusdisclosed but not claimed in this application, is disclosed and claimedin co-pending application Ser. No. 814,633, filed Apr. 9, 1969, in thenames of Cliiford J. Bell and Harold R. Moore, which application isassigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION Field of the invention I The inventionrelates in general to electrical transformers, and more specifically tonew and improved magnetic shielding means for transformers of theshell-form type.

Description of the prior art In electrical transformed of the shell-formtype, the pancake coils are substantially oblong in configuration,having straight outer sides, with contiguous sides being joined bycurved corners. Further each coil has an opening which has substantiallystraight sides in which the contiguous sides are also joined by curvedcorners. The pancake coils are assembled on a leg portion of a magneticcore structure, and, as is characteristic of the shell-form design, theyextend outwardly from opposite sides of the magnetic core structure.

In order to provide the functions of supporting the pancake coils andpreventing their movement due to short circuit stresses, clamping thelaminations tightly together in the tongue or leg portion of the corewhich extends through the coil openings, and supporting the pancakecoils in the proper assembled relation with the magnetic core structure,metallic coil support beams or members, and wedges are inserted throughthe openings in the coils at the top and bottom of the stack of corelaminations, between the magnetic core and the end portions of the coilopenings. Since these coil support members must support the weight ofthe pancake coils, they are made of metal, and in order to reduce theheating and losses in the support members, the more expensivenon-magnetic metals, such as stainless steel, are resorted to, in orderto provide the requisite strength without attracting leakage flux fromthe pancake coils. The leakage flux from the pancake coils isparticularly high, however, at the locations of these oil supports,requiring that even non-magnetic coil support members be shielded bybundles of laminations of grain 3,534,311 Patented Oct. 13, 1970oriented silicon steel. The bundles of laminations provide a lowreluctance path for the leakage flux adjacent the metallic coilsupports, and thus reduce heating and losses in the coil support membersdue to eddy currents. US. Pat. 2,370,045 discloses examples of theseprior art support and magnetic shielding structures.

While the magnetic shunts or shielding members of the prior art reducethe heating in the coil support members, stray or leakage flux heatingis still a problem in the larger transformer ratings, due to theincrease in the density of the leakage flux and the increase in the sizeand thickness of the metallic parts. Leakage flux heating is especiallysevere at the ends of the openings or windows in the pancake coils,where the coil support members and their shielding means are disposed,and particularly at the curved corners of the coil openings, where theflux density is the highest and where effective shielding by prior artmeans has not been achieved. The metallic support beam, the edges of themagnetic core, and the edges of the adjacent magnetic shunt, overheatadjacent the curved corners of the coil opening. The support beamoverheats because it is not shielded in this location, and the core andshield overheat because the flux does not strike the narrow edges of thecore and shield laminations perpendicularly, as required for minimalheating. This overheating has been made evident by discoloration of theedges of the metallic support beams, and other adjacent metallicmembers, in transformers which have been taken out of service anddisassembled. Overheating of metallic parts due to leakage flux is alsoevident due to the gassing of certain transformer units in service.

SUMMARY OF THE INVENTION Briefly, the present invention solves theproblem of openings, such as the metallic support beam, metallic wedges,magnetic shields constructed of laminated steel, and the corners of themagnetic core, by constructing spe cial magnetic shield members whichsnugly fit the curved corners of the coil openings, and which fill thespace between these curved corners and the adjacent metallic support andits shield members, and adjacent magnetic core. These magnetic shieldmembers for the curved corners of the coil openings are cast to shapefrom an insulating resin system, which is filled with magnetic fillermeans, such as metallic laminations, mangetic metallic shot, or magneticmetallic powder, or any combination of these materials. When metalliclaminations are used, they are aligned with their major surfacessubstantially perpendicular to the curved surface of the coil opening,to provide a low reluctance path for the leakage flux. These cast,specially shaped magnetic shunts fill the curved corners of the coilopenings with magnetic material and thus provide a low reluctance pathfor the leakage flux which protects the metallic support members, theirmagnetic shields, and the magnetic core, from overheating, and theysupport and uniformly compress the core laminations in areas which areunsupported in prior art arrangements.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of theinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIG. 1 is a fragmentary elevational view, in section, of an electricaltransformer of the shell-form type, constructed according to theteachings of the prior art;

FIG. 1A is an enlarged fragmentary view of a portion of the transformershown in FIG. 1;

FIG. 2 is a fragmentary view which illustrates how the prior arttransformer of FIG. 1 would be modified according to a first embodimentof the invention;

FIG. 3 is a fragmentary view which illustrates how the prior arttransformer of FIG. 1 would be modified according to another embodimentof the invention;

FIG. 4 is a perspective, partially cut away, of a transformer havingcertain magnetic shield members constructed according to the teachingsof the invention; and

FIG. 5 is a perspective view which illustrates a coil support andmagnetic shield member which may be used with the magnetic shieldmembers of the invention.

' DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings, andFIG. 1 in particular, there is shown an elevational view, in section, ofelectrical inductive apparatus 10, such as a transformer or reactor,which may utilize the teachings of the invention. Specifically,inductive apparatus includes a magnetic core-winding assembly 12disposed within a tank 14, which may be filled with a suitableinsulating and cooling dielectric, such as oil. The electrical bushingsfor bringing electrical conductors through the wall of the tank 14 forconnection to the windings therein, are not shown in order to simplifythe drawing.

The magnetic core-winding assembly 12 is of the shellform construction,having a plurality of pancake coils, such as pancake coil 16, disposedin inductive relation with a leg portion 17 of the magnetic corestructure 18. Magnetic core structure 18 has first and second similarassemblies or sections 20 and 22. Each of the magnetic core assemblies20 and 22 are formed of a plurality of metallic, magnetic laminations24, such as grain oriented silicon steel, which are stacked to form arectangular structure having at least four interconnected stack sectionsarranged to define at least one window or opening through which the coilturns may pass. The two assemblies 20 and 22 are disposed inside-by-side relation, with their adjacent stacked sections forming thewinding leg portion 17, about which the pancake coils are assembled.Thus, in the customary construction of shell-form power transformers,the pancake coils extend outwardly from the top and bottom surfaces ofthe magnetic core assembly 18.

The pancake coils, such as pancake coil 16, are each constructed of aplurality of turns 26 of electrical co-nductor, such as copper oraluminum, with the turns being insulated and wound to provide asubstantially rectangular configuration having rounded outer corners,and defining an opening 19 through which the winding leg portion 17 ofmagnetic core structure 18 may pass. The opening 19 in each of thepancake coils is also substantially rectangular in shape, havingsubstantially straight sides joined by curved corners 28, 30, 32 and 34.The pancake coils are disposed in side-by-side relation, with theiropenings in alignment, and they are interconnected to form the winding,or windings, of the electrical inductive apparatus or transformer 10.Transformer 10 may be single or polyphase, and it may be of the isolatedwinding, or of the autotransformer type.

In order to support the pancake coils, such as pancake coil 16, againstmovement in a direction parallel with the major surfaces of the pancakecoils, such as may tend to occur during short circuit conditions due todifferences in the locations of the electrical centers of the pancakecoils, which produces a force component parallel with the majorsurfaces, in order to support the pancake coils and insulating barriers,such as insulating barrier 36, and in order to clamp the laminations 24tightly together in the tongue or leg portion 17 of the magnetic coreassembly 18, support means is disposed to extend through the coils,between the coils and leg portion 17, at the upper and lower spacesdefined by the openings in the pancake coils and upper and lowersurfaces of leg portion 17. For example, as shown in FIG. 1, metallicT-beams 38 and 40, along with their magnetic shielding membersillustrated generally as a plurality of bundles 42 and 44 are providedat the upper and lower spaces, respectively. The bundles 42 and 44 areformed of a plurality of stacked metallic laminations which are weldedtogether, and which are then welded to the T-beams with the majorsurfaces of the laminations being perpendicular to the T-beams.

The metallic T-beams 38 and 40 extend through the coils and aresupported at their extreme ends outside the coils. Wedges, as required,are forced between the T-beams and pancake coils to compress thelaminations of the leg portion 17 tightly between the upper and lowercoil support members. The pancake coils and insulating barriers are alsopressed together in a direction perpendicular to their major surfaces,between end frame structures attached to the tank walls, to hold thepancake coils against movement due to the component of force generatedduring short circuit conditions which tends to separate the coils in adirection normal to their faces.

The leakage flux from the pancake coils has a high density adjacent thecoil support T-beams 38 and 40, with the flux density being especiallyhigh adjacent the rounded corners of the pancake coil openings. In orderto il1us trate the problem of shielding structures disposed adjacent therounded corners of the coil openings, the portion of the transformer 10shown in FIG. 1 which is within the circle A, is shown enlarged in FIG.1A. As illustrated in FIG. 1A the leakage flux, illustrated by lines 46,intersects the rounded corner of the coil opening substantiallyperpendicular to the curved surface. The leakage flux 46 causesoverheating of the T-beam 40 at its lateral edges, as it is difiicult toextend the bundles 44 of metallic laminations to the edges of the T-beamdue to the curvature of the coil opening. Further, the edges of legportion 17 and the edges of the bundle 44 of shielding laminations whichare adjacent corner 32 overheat, as the leakage fiux in this area doesnot strike the thin edges of these laminations perpendicular thereto.Therefore, eddy currents are created in the end laminations of theshielding bundles and the end laminations of the leg portion 17, whichcause excessive heating and losses in these areas.

The present invention solves the problem of overheating the metaldisposed adjacent the curved corners of the coil opening, by providingespecially shaped magnetic shunt members which closely conform to thecurved openings. The specially shaped magnetic shunt members provide alow reluctance shunt path adjacent the edges of the T-beam, its magneticshielding members, and magnetic core, to prevent the leakage flux fromentering these members and causing heating and losses due to eddycurrents.

A first embodiment of the invention is shown in FIG. 2, which is afragmentary view illustrating how the transformer 10 shown in FIG. 1would be modified according to this embodiment of the invention.Essentially, the fragmentary view shown in FIG. 2 is the same areaencompassed by the circle A of FIG. 1. Like reference numerals in FIGS.1 and 2 indicate like components. More specifically, FIG. 2 illustratesa special magnetic shielding member 50, which is formed of a castresinous insulating material 51, such as an epoxy resin system, which isfilled with magnetic material 52. The T-beam 40 shown in FIG. 1, isgiven the reference numeral 40', as it has a width which extends only tothe point where the coil opening starts to curve at its corners. Thesolid magnetic shielding member 50 now provides the support required forthe laminations 24 of the magnetic core leg portion 17 which washeretofore provided by the T-beam, and it additionally provides supportfor the laminations where they are unsupported by prior art structures.By reducing the width of the T-beam 40, it will extend approximately tothe same location as the outer edge of shielding bundle 44, which allowsthe magnetic shielding member 50 to be constructed with a flat surface53 which is disposed against the T-beam 40 and shielding bundle 44, aflat;

surface 55 which is perpendicular to the first flat surface 53, which isdisposed against the bottom lamination of the leg portion 17, and acurved surface 57 which closely conforms to the curved surface 30 of thecoil opening ing 19.

The resin system of which the magnetic shielding member 50 is formed maybe any suitable resin which will maintain its strength at the elevatedtemperatures to which it will be subjected during normal usage in thetransformer, and it should also be resistant to attack from the coolingfluid uilized in the transformer. In general, the resin should be athermo-setting resin, with the epoxy resins being excellent because oftheir excellent physical strength at ambient and elevated temperatures,and their resistance to attack from transformer oils and other coolantsutilized in transformers. Since suitable epoxy resin systems are wellknown in the art, it is not necessary to describe a specific epoxy resinsystem in detail.

In this embodiment of the invention, the magnetic shielding member 50 isfilled with metallic magnetic particles 52, such as metallic shot and/ormetallic powders. The metallic shot and powder should, in general, beselected to provide the maximum concentration of filler in the magneticshunt member 50, in order to provide a low reluctance magnetic circuit.The filler particles may be a uniform size, or they may be graded toprovide a predetermined range of sizes.

Suitable magnetic shunt members have been cast of epoxy resin filledwith 200 mesh powdered iron, utilizing the ratio of to parts of resin to80 to 90 parts of the powdered iron, by weight. They were formed in amold which had sufficient length to allow the resulting cast magneticshunt to be disposed through the entire length of the window of anelectrical phase, and to intercept or butt against magnetic wall shieldsdisposed on tank at either end. The mold shape closely conformed to theconfiguration of the opening into which the magnetic shunts were to beinserted, providing additional support for the tongue iron. Magneticshield members constructed in this manner have been very effective inpreventing heating of the steel parts separated from the flux source bythe magnetic shield members, and the shunts themselves experienced verylittle heating, which illustrates that they form a low reluctancemagnetic shunt circuit.

FIG. 3 is a fragmentary view which illustrates still another embodimentof the invention. FIG. 3 encompasses the same general area as thefragmentary view of transformer 1 shown in FIG. 2, and it illustrateshow the transformer of FIG. 1 would be modified according to thisembodiment of the invention. In this embodiment, instead of filling thespecially formed shunt member of discrete metallic particles, such asmetallic shot and/or powdered iron, the efficiency of the shunt isincreased by embedding oriented bundles of metallic laminations withinthe shield member. More specifically, as shown in FIG. 3, a speciallyformed magnetic shunt member 60 is cast in a special mold, utilizing aresin system 61, in which is embedded a plurality of bundles 62, eachformed of stacked laminations 64 which have been prebonded together toform coherent bundles of laminations. Each of the bundles 62 oflaminations contain a relatively small number of laminations, in orderto orient the laminations of each bundle substantially perpendicular tothe curved surface of the corner of the opening in the pancake coils.For example, it has been found that bundles formed of one-half inch wideelectrical steel laminations having a thickness of .012 inch, with thebundles having a build dimension of one-half inch, are very effective inproviding a low reluctance magnetic shunt 60. The bundles of laminationsmay be formed by stacking a large plurality of laminations together andpainting their edges with an epoxy resin, or other suitable resinsystem, and allowing the resin system to harden. Bundles having thedesired number of laminations may then be cut using a sharp tool, fromthe bonded laminations, and they may then be placed in a mold which isfilled with a resin system. The resin system should also be filled withdiscrete magnetic particles, such as powdered iron or shot 66, thespecially formed cast magnetic shunt member 60, may be utilized with theconventional coil supporting structure shown in FIG. 2, or, as shown inFIG. 3, it may be used with the new coil support and magnetic shuntmember 54, which will be hereinafter described, and which is claimed inthe hereinbefore mentioned copending application. The cast magneticshunt member 50 shown in FIG. 2 may also be used with the coil supportand magnetic shunt member 54.

FIG. 4 is a perspective view of a transformer 70, which illustrates theplacement of the specially formed magnetic shunt members, such as shownin FIGS. 2 and 3, adjacent the rounded or curved edges of the openingsin the pancake coils, as well as illustrating a new and improvedmagnetic shielding structure which may be utilized with the speciallyformed corner shield members. Specifically, transformer 70 includes amagnetic corewinding assembly 72 disposed within a tank 84, which may befilled with a suitable insulating and cooling fluid, such as oil. Themagnetic core-winding assembly 72 includes a plurality of pancake coils74 disposed in inductive relation with a magnetic core structure 76.Magnetic core structure 76 is formed of first and second magnetic coresections 78 and 80 which are disposed in sideby-side relation to providea leg portion 82 about which the pancake coils 74 are assembled.

The tank 84 is of the form-fit construction, having a lower portion 83which closely conforms to the outer configuration of the lower extensionof the pancake coils 74 from the magnetic core 76, and which includes ashelf 87 upon which laminations 77 are stacked in superposed relation toform the magnetic core sections 78 and 80. The laminations 77 of themagnetic core sections 78 and 80 are compressed tightly together againstshelf 87 by end frame members, such as end frame members 86 and 88,which are welded to the inside of the upper portion 89 of tank 84. Theclose proximity of the lower tank walls 83 and end frame members 86 and88 to the pan cake coils 74 provides a low reluctance path for theleakage flux from the coils, making it necessary to magnetically shieldthese components in order to prevent heating and losses therein.

In the prior art, the tank walls and end frame members are shielded withbundles of metallic laminations which are attached to the walls and endframe members, and which form magnetic circuits by butting the ends ofthe bundles of laminations together. However, the tolerances of thebundles, and the tolerances of the end frame members and tank make itdifficult to obtain good butt joints between the ends of the bundles oflaminations, with substantial gaps thus being introduced into themagnetic circuit. These gaps increase the reluctance of the circuits andreduce the efiiciency of the magnetic shunts.

In addition to shielding the tank walls and end frame members from theleakage magnetic flux from the plurality of pancake coils, in the priorart the coil support members are magnetically shielded, as hereinbeforedescribed relative to FIG. 1. The bundles of metallic laminations areassembled by Welding across the edges of the laminations, and then thebundles of laminations themselves are welded to the metallic T-beam orsupport members. The welds across the edges of the magnetic steellaminations adversely affect their magnetic properties, which increasesthe reluctance of the magnetic circuits, and it would thus be desirableto be able to assemble the laminations into bundles and fix the locationof the bundles, without resorting to welding. FIG. 4 illustrates new andimproved magnetic shielding assemblies which perform the functions ofsupporting the pancake coils, and of providing low reluctance magneticcircuits between the leg portion of the magnetic coil structure and thepancake coils, and between the pancake coils and the tank and end framemembers of the transformer.

More specifically, the new and improved magnetic shielding structuresinclude lower and upper magnetic shielding assemblies 90 and 92,respectively. The lower magnetic shielding assembly 90 includes aplurality of bundles 94 of laminations 95, which extend in an insulatingmanner through the pancake coil openings, between the lower surface ofthe leg portion 82 and the lower end of the openings in the pancakecoils 74. The separate metallic support member or T-beam is eliminatedby constructing the bundles 94 to have the strength necessary to supportthe pancake coils 74. The bundles 94 of metallic, magnetic laminationsare placed side-by-side across the bottom surface of the pancake coilopenings, on the fiat portion of the coil opening, with the major planesof the laminations being perpendicular to the adjacent edges of the coilopenings. The rounded or curved edges of the coil opening may be filledwith specially formed magnetic shunt members 97 and 99, which aid insupporting the laminations of the leg portion of the magnetic core, aswell as providing a low reluctance path for the leakage flux which isperpendicular to the curved edges of the coil openings. The speciallyformed magnetic shunt members 97 and 99 are formed of a cast resinsystem filled with magnetic metallic material, as hereinbeforedescribed.

The bundles 94 of laminations 95, as well as the specially preparedmagnetic shunt members 97 and 99, have their ends at one side of thecoils 74 disposed adjacent the ends of a plurality of bundles 96 oflaminations 101, which bundles are disposed perpendicular to the bundles94, and which extend towards the bottom 85 of the tank 84. The majorplanes of the laminations 101 are perpendicular t the insulating barrier103 disposed at the end of the stack of coils 74. The other ends of thebun dles 94, and the other ends of the special magnetic shunts 97 and 99are disposed adjacent the ends of similarly disposed bundles oflaminations (not shown) at the opposite side of the coils 74.

In order to connect the ends of bundles 94 and 96 with a low reluctancejoint, the laminations of bundles 94 and 96 may be staggered to providetongue-andgroove joints, which have a very low reluctance, even when thetongue-and-groove joints are not completely closed. Thus, a liberaltolerance may be utilized while constructing the bundles of laminationsand the noncritical portions of the transformer, without substantiallyaffecting the losses of the magnetic circuit.

The tank bottom 85 is shielded from the leakage flux from pancake coils74 by a plurality of bundles 98 of laminations 105 which extend betweenthe lower extremity of the pancake coils 74 and the tank bottom 85, andwhich are magnetically linked with the perpendicularly disposed bundlesat each end of the stacked coil assembly, such as the bundles 96. Thebundles 98 may be joined to the perpendicularly disposed bundles withtongue-and-groove joints, similar to the connection of the bundles 94 tothe perpendicularly disposed bundles at each end thereof. Thus, there isa complete magnetic circuit or loop which encircles the lower portion ofthe pancake coils 74, which extends through the coil opening to shieldthe tongue iron from the leakage flux, it extends along the walls of thelower tank portion 83 to shield the adjacent walls from the leakage fluxfrom the pancake coils, and it also extends across the bottom of thetank 84, between the bottom 85 and the pancake coils 74.

The lower shielding structure '90 also includes a second completemagnetic loop or circuit which encircles the lower portion of thepancake coils 74 perpendicular to the axis of the first magnetic loop orcircuit. This magnetic loop protects the remaining side wall portions ofthe lower tank portion 83 from leakage flux from the bottom extension ofthe pancake coils 74 below the mag- 8 netic core structure 76. Morespecifically, the second magnetic loop portion of the lower magneticshielding assembly includes a plurality of bundles 102 of laminations107 which have their adjacent ends insulatingly butted against the outerlamination of the adjacent outer bundle of the bundles 96 oflaminations. In like manner a pluarlity of bundles 106 are disposedperpendicularly to the bundles 96, with the adjacent ends of the bundles106 being insulatingly butted against the outer lamination of the bundleat the other outer side of the bundles 96. The bundles are magneticallyjoined to a plurality of bundles104, such as by a tongue-and-groovejoint, which bundles extend along a lower vertical transformer wall,parallel with the tank bottom 85, between the pancake coils and theadjacent transformer wall, to where their other ends are joined with aplurality of bundles disposed similar to the bundles 102. These bundlesthen have their ends butted against the bundles at the other end of thetransformer which are similar in location to the bundles 96. In otherwords, bundles 102 and 104 are part of a substantially U-shapedstructure 121 which is fitted about one end of the lower extension ofthe pancake coils 74 below the magnetic core 76, with the legs of the U-shaped structure 121 being butted against the vertically disposedbundles of laminations at opposite ends of the coils 74.

The bundles 106 are magnetically linked with a plurality of bundles 108,such as with tongue-and-groove joints, which extend along the adjacentlower vertical transformer wall to protect this wall from the leakageflux from the pancake coils 74. The bundles 108 join a plurality ofbundles disposed similar to bundles 106,'except at the other end of thecoils, such as with tongue-andgroove joints, which bundles extendperpendicularly against the bundles at the other end of the transformerwhich are disposed similar to bundles 96. Thus, bundles 106 and 108 arepart of another U-shaped structure 123, which, along with the otherU-shaped structure 121, and the vertically disposed bundles, from acomplete magnetic circuit about the sides and ends of the lowerextension of the pancake coils 74, which protect the bottom portion 83of the transformer tank 84 from overheating due to stray leakage flux.

The upper shielding assembly 92 is similar to the lower shieldingassembly 90, except the magnetic circuit which extends through the coilwindows is not completed across the top of the coils, since it mayinterfere with leads and accessories disposed above the pancake coils.Further, it is unnecessary to shield the top of the pancake coils, asthe top of the tank 84 is not immediately adjacent the top of thepancake coils. More specifically, the upper shielding assembly 92includes a plurality of bundles shown generally at 112 which extendthrough the coil openings, between the upper ends of the openings in thepancake coils 74 and the upper surface of the magnetic core structure76, with the adjacent ends of the bundles 112 at one end of the stackedcoil assembly being joined to the ends of bundles which are disposedperpendicularly upward from the bundles 112, and with their remainingadjacent ends being joined to similarly disposed bundles at the oppositeend of the stacked coils, to shield the end frames at opposite ends ofthe transformer. Two substantially U-shaped structures and 127, similarto the U-shaped structures 121 and 123, are disposed about oppositesides of the upper extensions of the pancake coils 74, with the ends ofthe U-shaped structures 125 and 127 butting against the perpendicularlydisposed bundles of laminations at opposite ends of the transformer,such as the bundles 110. The first U-shaped structure 125 includes aplurality of bundles 114 which are butted against the perpendicularlydisposed bundles 110, a plurality of similarly disposed bundles at theopposite side of the transformer (not shown), and a plurality of bundles137 which connect the ends of these bundles, such as withtongue-and-groove joints.

The second U-shaped structure 127 includes a plurality of bundles 11'5disposed with their ends perpendicular to the plurality of bundles 110,a plurality of similarly disposed bundles at the other end of thetransformer (not shown), and a plurality of bundles 116 which connectthe ends of these bundles, such as with tongue-andgroove joints.Therefore, the upper shielding structure 92 provides a low reluctancepath for the leakage flux within the coil openings, and also a lowreluctance path for the leakage flux which protects the end framemembers from the leakage flux of the pancake coils.

FIG. is a perspective view of bundles 120 and 122 of laminations 125,which are constructed to enable the bundles to achieve the structuralstrength required to eliminate the T-beam or coil supports disposed inthe upper and lower coil openings, between the coil openings and thetongue or leg portion of the magnetic core structure 76. As illustratedin FIG. 5, the bundles 120 and 122 are formed such that they may bejoined with tongue and groove joints, with either in-line or angularconnections between the two bundles. Bundle 120' includes a plurality oflaminations 132, 128, and 124 of similar length, separated by aplurality of laminations 126 and 130 of a shorter length, in order toprovide the tongueand-groove ends which will mate with thetongue-andgroove ends fo bundle 122. In this embodiment the looselaminations are wrapped tightly with a woven fabric tape 131, such as acotton or glass tape, and the ends of the tape are temporarily securedwhile the entire tape area is coated and impregnated with a lowviscosity resin 133, which is then cured. The low viscosity resin 133,which is preferably a thermosetting resin, penetrates the woven fibersof the fabric tape 131, and penetrates the stacked laminations for ashort distance, which, upon curing, bonds the laminations into acoherent bundle having an integrity and strength greater than thebundles of the prior art which are welded across their edges to obtainthe desired assembled relation. Instead of impregnating the tape andlaminations after assembly, the material of which the laminations areformed, and the tape, may be pre-treated with resin, which is dried butnot cured. Then, after the laminations are cut, stacked, and taped, theassembly is heated to flow the resin and cure it to a solid.

The adhesive or resin coating 133 may be any suitable resin which willmaintain its strength at the elevated temperatures to which it will besubjected during normal usage of the transformer, and it should also beresistant to attack from oils and other dielectric fluids used withinthe transformer. Epoxy resins have been found to be excellent, becauseof their strength at elevated temperatures, and their resistance toattack from transformer oils and other chemicals. In addition to forminga solid high strength bundle of laminations, the impregnated and curedresin-tape structure provides the insulation required between the shieldmembers and adjacent portions of the transformer.

While the bundles of laminations for shielding the end frames and tankof the transformer have been illustrated as being assembled and mountedon the pancake coils 74, it will also be evident that these magneticshielding structures may be connected to the end frames and tank wallsby suitable clips which are sized to hold the bundles, and which arewelded to the end frames and tank walls.

In summary, there has been disclosed new and improved magnetic shieldingmembers which are disposed at the curved corners of the coil openings toprotect the coil support members, the coil support shielding means, andthe adjacent leg portion of the magnetic core, from overheating due tothe leakage flux entering the curved corners of the coil opening. Thenew and improved magnetic shunt members are formed to the desired shapefrom a cast resinous insulation system, which is filled to a high degreewith magnetic material, such as laminations, shot, and/or powdered iron.In addition to effectively shielding an area which is unshielded inprior art structures, the new and improved shielding members providesupport for the laminations of the leg portion of the magnetic core,where the laminations have been un supported in prior art structures.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings shall beinterpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. An electrical transformer comprising:

a magnetic core having a leg portion,

a plurality of electrical coils, each of said electrical coils having anopening defined by substantially straight sides joined by curvedcorners, said plurality of coils being positioned on said leg portion,

a plurality of magnetic shield members extending within said coils,between said coils and said leg portion, said magnetic shield membersbeing spaced from one another, with each being adjacent a curved cornerof the coil openings, said magnetic shield members being formed of acast resinous insulating material filled with magnetic filler means,said magnetic shield members being shaped to closely conform to theadjacent leg portion and the curvature of the adjacent curved corner ofthe coil openings,

and support means extending within said coils, between said coils andsaid leg portion.

2. The electrical transformer of claim 1 wherein the opening in eachcoil has four sides and four curved corners, with a magnetic shieldmember being disposed adjacent each of the curved corners.

3. The electrical transformer of claim 2 wherein the support meansincludes first and second structures disposed between the leg portionand the coils, adjacent first and second predetermined opposite sides ofthe coil openings, respectively, and between the magnetic shield membersdisposed adjacent the curved corners contiguous to these predeterminedopposite sides of the coil openings.

4. The electrical transformer of claim 1 wherein the support meansincludes a metallic body portion disposed adjacent the leg portion, andmagnetic shielding means disposed between the metallic body portion andelectrical coils.

5. The electrical transformer of claim 1 wherein the support means arebundles of metallic laminations, assembled and insulated to provide thesupport required for the coils, while also functioning as additionalmagnetic shields.

'6. The electrical transformer of claim 1 wherein the magnetic fillermeans of the cast resinous magnetic shield members includes finelydivided iron particles.

7. The electrical transformer of claim 1 wherein the magnetic fillermeans of the cast resinous magnetic shield members includes a pluralityof stacked metallic laminations arranged with their major planessubstantially perpendicular to the curvature of the comers of the coilopenings.

8. The electrical transformer of claim 7 wherein the magnetic fillermeans also includes finely divided iron particles.

References Cited UNITED STATES PATENTS 1,610,867 12/1926 Lennox 336-2121,763,150 6/1930 Hebnew 336-219 2,370,045 2/1945 Keto 336-84 3,281,74510/1966 Moore et al. 336-84 3,464,041 8/ 196 9 Waterman 336-84 XR THOMASJ. KOZMA, Primary Examiner US. Cl. X.R. 336-212, 215, 216

